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Saturday, 23 April 2016

Practical Application - Modulation Techniques

Signal from device generated is known as base band signal which is not directly transmitted to the desired place but it is modulated before feeding the signal to transmitter. Modulation is a technique of varying any component of carrier signal in proportion to that of base band signal. In this article I have covered several Analog and Digital modulation techniques. Mentioned its basic definition with figure and the important thing, practical application of that modulation technique.So lets go into brief description and application of some of the techniques.

AmplitudeModulation

In the simplest way possible, AM can be explained as changing Amplitude of the carrier signal or the high frequency signal with respect to the modulating signal.

Application

1.It is used in Aircraft for communicationbetween station to pilot and vice versa. So why didn't they opt for FM which is less affected to noise as compared to AM. The reason I found is that, AM is used so that multiple stations on the same channel can be received. While in FM, reception of weaker signal is blocked by the stronger signal which is normally known as capture effect.

2.It is still used in commercial radio broadcasting. But AM having Low frequency, they only broadcast the commentary or news or we can say only vocals will be their. As the frequency is increased, in ground wave propagation attenuation will increase. Hence FM having higher frequency will get more degraded in ground wave as compared to AM. But still use of FM is more than AM. Because it uses direct wave propagation(line of sight).

Frequency Modulation

In case of frequency Modulation, the frequency of Carrier is varied with the instantaneous value of modulating signal.Advantage of FM over AM is that it has ability to reject the noise or in the other way, noise doesn't affect much in FM.

Applications

1.The most common application which I don't thing any of you is not aware of this. i.e. FM Radio broadcasting.

2.It was surprise for me also to know that, FM was used in VCR tape recorder. For storing Luminance i.e. the black and White portion of the video is recorded by FM modulation in this analog Tape while the color part is directly recorded by the base band signal. I didn't got more data in this but I came to know that it uses FM for recording.

Quadrature Amplitude Modulation

Till now we have seen that, only single parameter is changed with the instantaneous value of base band signal. But in QAM, two parameters of the signal are changed Amplitude and Phase. In short, QAM is made up of AM and PM. QAM is also known as QPSK(Quadrature Phase Shift Keying) which can be treated as mixture of ASK(Amplitude Shift Keying) and PSK(Phase Shift Keying).

QAM can be of different types depending upon the number of possibilities of Amplitude and Phase.

For Eg. I have shown two fig. in which first is 8-QAM (2 diff. Amplitude & 4 diff. Phase), and the second fig. is 16-QAM ( 4 diff. Amplitude & 4 diff Phase).

Applications

1. NTSC and PALare color encoding techniques used in analogue TV and both these encoding techniques uses QAM modulation for encoding the luminance and chrominance information combinedly, for composite video signal.

Till now, the modulation techniques were used for analog signal, but now the modulation techniques we will discuss are used in digital signal modulation. First is ASK, it is very much similar to AM, in which Amplitude of the carrier is varied in proportional to the digital base band signal. As digital signal is a binary signal, so we will have only 2 different amplitude value in ASK. ASK modulation is shown below.

Applications

1.ASK Modulation is used inRF Modules. I have used this module many time for making wireless robo car. We need to attach Encoder and Decoder IC to code decode the data. And the digital data from the Encoder is modulated by ASK and than it is transmitted.

2. Some of the RF remotesand RF car keys also uses ASK modulation for transmitting digital data over air. While studying about RF car keys, I found that in some of the car keys, every time the button is pressed different data is transmitted so that one can't just simply copy and transmit the same data to unlock the car.

On Off Keying

On Off Keying(OOK) modulation technique is similar to that of ASK. Difference is that in On Off keying, binary '0' is represented by 0 volt while binary '1' is represented by some fixed amplitude. And frequency in both the cases will be same as carrier frequency.

Application

1. This modulation technique is used only for low data transfer rate around 100 bits per second. One application of this technique which we use daily is in IR Remote Control. That remote can be of TV, AC, Radio etc. It works on 38 kHz carrier frequency.

Frequency Shift Keying

FSK can be related with FM. But this modulation technique is used on digital modulation. In this, frequency of the carrier is changed in accordance with the data bit. For digital '1' frequency will be high while for digital '0' frequency will be low. FSK modulation technique is shown in below fig.

Applications

1.Bluetooth or BLE(Bluetooth Low Energy)which normally used everywhere like in mobile phone, wireless speakers, Laptops, etc usesGFSK( Gaussian Frequency Shift Keying ) modulation technique for data transmission. Difference between GFSK and FSK is nothing but GFSK has an additional Gaussian Filter to reduce the side band power.

Phase Shift Keying

In phase shift keying, phase of the carrier is changed in accordance with the data or base band signal. For digital data '1', phase shift will be 180 degree while for digital data '0', phase shift will be 0 degree.

QPSK Modulation

Application

1. WiFihas different versions based upon different IEEE standards. Different versions have different speeds and also uses different modulation Techniques. Out of them IEEE 802.11b uses QPSK modulation and 802.11a and g uses 16 or 64 QAM modulation for transmission. Difference between this two is the speed of data transfer. Obviously, 64-QAM is faster than QPSK.2.Enhanced version of GSM is known asEDGE ( Enhanced Data rates for GSM Evolution ) uses 8-PSK modulation technique for faster data transfer as compared to GSM. GSM uses only 1 bit per symbol for data transfer while EDGE uses 3 bits per symbol for data transfer. It is commonly called as 2.75G network

Minimum Shift Keying

MSK modulation can be compared with PSK modulation but the difference between them is, in MSK their is no abrupt change in the phase of the carrier signal, rather their is very smooth transition between different phases. It looks similar to that of FSK.

Application

1.MSK is used with Gaussian filter ( commonly known as GMSK ) is used in GSM mobile communication or 2G network. Gaussian filter is used to reduce the side band power of the spectrum. It's data transfer rate is only 1 bit per symbol. Enhanced version of GSM was developed which is known as EDGE( Enhanced Data rates for GSM Evolution ) which uses 8-PSK modulation which uses 3 bits per symbol, faster than GSM.

2.Ships uses GMSK modulation technique for communication with other ships as well as the station. Data like speed of the ship, its current position, Estimated Arrival Time, Type of the ship etc is constantly transmitted through Time division multiplexing. This Tracking system is known as Automatic Identification System (AIS).

This much of data I got when I was researching the topic "Application of modulation techniques". If you know something more than this, do share it with others by commenting below.